The present invention in general relates to a novel scanning force microscopy method. More specifically, it relates to a method for characterizing magnetic fields. Still more specifically, the present invention relates to such a method using magnetosensitive materials. The invention relates also to a device for carrying out such a method as well as to a novel scanning probe to carry out the method according to the invention.
With the continuously increasing recording density in magnetic storage media and the continual improvement in quality of magnetic heads in recent years it has become ever more important to be able to measure the spatial distribution of a magnetic field as accurately as possible, since this distribution in the vicinity of the gap in a magnetic head represents a factor which has a profound influence on the recording, overwrite and playback properties.
Magnetic writing and recording heads are therefore a field of intense research and development that requires extremely sensitive techniques to estimate device parameters for further miniaturization. In addition, it is desirable for process control that scientific and technical feedback for manufacturing parameters are enabled as early as possible in the production process, in particular on a row or even on wafer level. Micro- and nanostructures are often characterized by scanning probe Microscopy (SPM) in research as well as in analytical disciplines for online quality control and failure analysis. SPM can attribute different but specific functionalities that allow a characterization of various surface properties, e.g. surface roughness, conductivity variations, magnetism, hardness, thermal and friction phenomena on the nanometer scale. In storage industries, magnetic force microscopy (MFM) techniques have been used to characterize magnetic storage disks and thin-film magnetoresistive recording heads. Equally, micrometersized magnetic writing heads are a major technology undergoing miniaturization to realize smaller bit sizes and thereby higher areal density in the magnetic recording media.
Techniques to image magnetic properties are based on electron microscopy such as spin polarized scanning electron microscopy (cf. R. Allenspach, Physics World, 7, 45 (1994)), Lorentz microscopy (cf. X. Portier et al., Appl. Phys. Lett., 71, 22032 (1997)), Magnetic Force Microscopy (cf. Y. Martin and H. K. Wickramasinghe, Appl. Phys. Lett. 50, 1455 (1987)), Spin Polarized Electron Tunneling Microscope (cf. Z. Wu et al., Surface Science, 386, 311 (1997)) Scanning Near Field Magnetooptical Microscopy (cf. U. Hartmann, Journal of Magnetism and Magnetic Materials, 157/158, 545 (1996)) and Kerr microscopy (A. Hubert and R. Schafer,. Magnetic Domains, The Analysis of Magnetic Microstructures, New York 1998).
In particular in MFM, one mode is to resonate the magnetic sensor via a bimorph and to detect phase shifts owing to variable magnetic forces. Another mode, which is used to characterize write elements, is to excite MFM sensor vibrations via the variable magnetic field of the write element. In this mode the vibrational characteristics of the MFM sensor changes in dependance of its position above the write element. Both techniques feature a high lateral resolution (approx. 50 nm), but the high magnetic field generated by the write element can cause the magnetic tip to touch the surface, resulting in imaging errors (hereinafter referred to as artifacts). In addition, magnetic fields above the coercive field of the scanning tip alter its magnetic moments. The latter can cause severe imaging errors (hereinafter referred to as artifacts) and may lead to a misinterpretation of measured device parameters.
It is therefore an object of the present invention to provide a method to characterize magnetic fields and magnetic properties of microstructures that do not suffer from the above mentioned artifacts.
It is a further object of the invention to characterize such magnetic fields emanating from micrometer-sized devices, especially from magnetic read/write heads (RWH) used in storage technology.
It is still a further object of the present invention to characterize the magnetic fields using a non-magnetic, standard tip as a local probe.
Further advantageous embodiments of the invention are contained in the dependent claims.